Conventionally, as means for detecting presence or absence of metal powders floating in a lubrication oil, there is known means for detecting the mixing of the metal powders by adsorbing the metal powders by a magnet disposed, for example, on a bottom wall of an oil tank and detecting the change of magnetic flux at this time.
In the above conventional floating metal powder detecting means, the detecting means are disposed in a spot-like manner to the oil tank, and the detecting ability of one detecting means is limited. Accordingly, when it is required to perform the detection over a wide range, the provision of a large number of detecting means is inevitably required. The increasing of the location positions of the detecting means results in a problem of complicated detecting control thereof. Furthermore, in the above conventional detecting means, it is impossible to utilize the detecting means in a case where the metal powder is small in size and its mixed amount is relatively small such as several tens to several thousands PPM.